Water splitting to form hydrogen and oxygen over a heterogeneous photocatalyst using solar energy is a promising process for clean and renewable hydrogen production. In recent years, numerous attempts have been made for the development of photocatalysts that work under visible light irradiation to efficiently utilize solar energy. This article reviews recent research progress in the development of visible light-driven photocatalysts, focusing on the refinement of oxynitride materials. They harvest visible photons (~450–700 nm) and work as stable photocatalysts for water reduction and oxidation under visible light. Oxynitrides with d0 electronic configuration can be successfully applied to a two-step water-splitting system, which can harvest a wide range of visible photons (~660 nm), in the presence of an iodate/iodide shuttle redox mediator. Also d10-type oxynitrides of GaN–ZnO and ZnGeN2–ZnO solid solutions can achieve functionality as photocatalysts for overall water-splitting under visible light without noticeable degradation.

Micro- and nanostructures are found widely in nature and are important for the development and maintenance of organisms. Fabricated structures of dimensions corresponding to native biological structures may be obtained by methods such as laser-based fabrication and are of special relevance to applications in biology and medicine, as they impact cellular behavior. In this review, we will examine how fabricated structures of a particular length scale interact with natural structures of corresponding dimensions to produce the designed response, thus giving readers a primer on how laser-based fabrication may be fruitfully applied to biomedicine. Lasers have been used to fabricate nanopores for a variety of applications at the molecular level, such as the analysis of DNA. At the subcellular level, microstructures such as elastic beams fabricated by laser direct writing have been used to adhere and interact with cells. In the area of tissue engineering, an important application of micro- and nanostructures is related to their ability to control intercellular interactions. The fabricated structures facilitate the positioning of cells with respect to each other, so as to simulate the complexity of native tissues. Focused laser sources have also been used to create channels modified with functionalities to help guide cell migration.

Effective schemes to address contact resistance between silicide and a highly doped diffused junction are examined. Some of the techniques introduced include (1) metal work function tuning, (2) interfacial dipole engineering, and (3) phase modulation of the nickel silicide. These techniques allow modulation of the Schottky barrier of NiSi to n-Si to less than 0.3 eV, which is crucial to achieve sub 10−8 Ω cm2 contact resistivity for the sub-32 nm technology node.

To harness the full spectrum of solar energy, optical reflections at the surface of a solar photovoltaic cell must be reduced as much as possible over the relevant solar spectral range and over a wide range of incident angles. The development of antireflection coatings embodying omni-directionality over a wide range of wavelengths is challenging. Recently, nanoporous films, fabricated by oblique-angle deposition and having tailored- and very low-refractive index properties, have been demonstrated. Tailorability of the refractive index and the ability to realize films with a very low-refractive index are properties critical in the performance of broadband, omnidirectional antireflection coatings. As such, nanoporous materials are ideally suited for developing near-perfect antireflection coatings. Here, we discuss multilayer antireflection coatings with near-perfect transmittance over the spectral range of 400−2000 nm and over widely varying angles of acceptance, 0−90°. The calculated solar optical-to-electrical efficiency enhancement that can be attained with nanoporous multilayer coatings over single-layer quarter-wave films is 18%, making these coatings highly attractive for solar cell applications.

Starch is an abundant, biodegradable, renewable, and low-cost commodity that has been explored as a replacement for petroleum-based plastics. By itself, starch is a poor replacement for plastics because of its moisture sensitivity and brittle properties. Using starch as a fermentation feedstock, various promising biodegradable plastic products have been developed that rival petroleum-based plastics and are poised to enter the marketplace or are already in production. Other starch-based plastics are blends with other compatible resins or are based on chemical treatments that improve the functional properties of various products. While these approaches are very promising, there are efforts under way to develop viable products from starch by using different processing technologies and by combining starch with other materials to make functional composites. This article focuses on different technologies for making starch-based foam materials and the use of reinforcing fibers and nanoparticles for making composites that can substitute for some petroleum-based foam products.

Water splitting to produce H2 using sunlight is a form of artificial photosynthesis in that light energy is converted to chemical energy. As such, water splitting using powdered photocatalysts has attracted attention in the framework of energy and environmental issues. This article reviews z-scheme photocatalyst systems for water splitting under visible light irradiation, especially focused on the systems consisting of SrTiO3:Rh of a H2-evolving photocatalyst, and O2-evolving photocatalysts with and without electron mediators. These photocatalyst systems showed activities for water splitting into H2 and O2 in a stoichiometric amount under visible light irradiation and even under sunlight irradiation. The photocatalytic activity was sensitive to pH. The optimum pH was 2.4 when iron ions were used as electron mediators. Co-catalysts also affected the activity. The photodeposited Ru co-catalyst gave an excellent performance. The best performance achieved by the pH adjustment and the selection of a co-catalyst was obtained mainly by suppression of back reactions to form H2O from evolved H2 and O2.

This article reviews the physical and chemical constraints of environments on biofilm formation. We provide a perspective on how materials science and engineering can address fundamental questions and unmet technological challenges in this area of microbiology, such as biofilm prevention. Specifically, we discuss three factors that impact the development and organization of bacterial communities. (1) Physical properties of surfaces regulate cell attachment and physiology and affect early stages of biofilm formation. (2) Chemical properties influence the adhesion of cells to surfaces and their development into biofilms and communities. (3) Chemical communication between cells attenuates growth and influences the organization of communities. Mechanisms of spatial and temporal confinement control the dimensions of communities and the diffusion path length for chemical communication between biofilms, which, in turn, influences biofilm phenotypes. Armed with a detailed understanding of biofilm formation, researchers are applying the tools and techniques of materials science and engineering to revolutionize the study and control of bacterial communities growing at interfaces.

Outreach efforts within the materials science community include learning goals or outcomes designed with the purpose of increasing awareness or interest in the field, improving the learning or achievement of subject matter, or even supporting a type of literacy or understanding. These outcomes need to be defined and measured. To demonstrate the success of an outreach activity, an appropriate assessment scheme must be implemented to determine how effectively the goals have been met. Assessment of K–12 outreach is presented in this article using the framework of a K–12 engineering design cycle of Ask, Imagine, Plan, Create, and Improve. Links will be drawn from among the “Ask,” “Imagine,” and “Plan” phases to the development of objectives and the establishment of the assessment plan. The “Create” and “Improve” phases will be connected to data collection and analysis techniques. Three forms of evaluation are discussed—formative, summative, and interim—as well as four areas of knowledge—cognitive, affective, behavioral, and metacognitive. Finally, this article lists some common pitfalls to avoid when considering these issues in the planning and reviewing of programs that will make assessment of K–12 outreach efforts a more positive and rewarding endeavor.

Over the past 10 years, the number of materials that can be processed by atomic layer deposition (ALD) has expanded rapidly. Significant progress has been seen in ALD of high-κ oxides, ternary oxides, and noble metals, which have been studied quite extensively. High-κ oxide processes are used today in various industrial applications. However, many new applications are pushing the need for less common compounds, and therefore new processes are being developed (e.g., for fluorides, Li containing compounds, and phosphates). New ALD processes require new designs for volatile precursors to deliver elements with ligands that ensure self-limiting surface reactions. In addition to inorganics, new polymeric and inorganic-organic hybrid materials are opening new frontiers for ALD, including expansion of the process to include molecular layer deposition. A combination of inorganic and organic parts in the deposited layers offers expanding opportunities for tailoring materials properties.

In this article, we review the reasons why high-temperature cuprate superconductors are inadequate for electric power applications, above liquid nitrogen temperatures, and examine the underlying causes. The most important reason is their low superconducting Cooper pair density, which for thermodynamic reasons reduces the theoretical maximum critical current density. We also discuss how low pair density (and high anisotropy) increase thermodynamic phase fluctuations of the macroscopic quantum pair wave function, which in turn leads to a limitation on the transition temperature itself. Finally, we discuss how, in highly correlated superconductors, there may be a conflict between the conditions necessary to achieve high transition temperatures in the face of phase fluctuations and the conditions necessary to produce strong pairing interactions.

High-energy cathode materials with high working potential and/or high specific capacity are desired for future electrification of vehicles. In this article, we provide a general overview of advanced high-energy cathode materials using different approaches such as core-shell, concentration-gradient materials, and the effects of nanocoatings at the particle level to improve both electrochemical performance and safety. We also summarize the methods used to prepare these materials. Special attention is placed on the co-precipitation process for making dense, spherical particles for the purpose of improving the powder packing density and increasing the electrode energy density.

The behavior of nuclear fuel in a reactor is a complex phenomenon that is influenced by a large number of materials properties, which include thermomechanical strength, chemical stability, microstructure, and defects. As a consequence, a comprehensive understanding of the fuel material behavior presents a significant modeling challenge, which must be mastered to improve the efficiency and reliability of current nuclear reactors. It is also essential to the development of advanced fuel materials for next-generation reactors. Over the last two decades, the use of density functional theory (DFT) has greatly contributed to our understanding by providing profound information on nuclear fuel materials, ranging from fundamental properties of f-electron systems to thermomechanical materials properties. This article briefly summarizes the main achievements of this first-principles computational methodology as it applies to nuclear fuel materials. Also, the current status of first-principles modeling is discussed, considering existing limitations and drawbacks such as size limitation and the added complexity associated with high temperature analysis. Finally, the future role of DFT modeling in the nuclear fuels industry is put into perspective.

Metals possess the highest conductivity among all room-temperature materials; however, ultrathin metal films demonstrate decent optical transparency but poor sheet conductance due to electron scattering from the surface and grain boundaries. This article discusses engineered metal nanostructures in the form of nanogrids, nanowires, or continuous nanofibers as efficient transparent and conductive electrodes. Metal nanogrids are discussed, as they represent an excellent platform for understanding the fundamental science. Progress toward low-cost, nano-ink-based printed silver nanowire electrodes, including silver nanowire synthesis, film fabrication, wire-wire junction resistance, optoelectronic properties, and stability, are also discussed. Another important factor for low-cost application is to use earth-abundant materials. Copper-based nanowires and nanofibers are discussed in this context. Examples of device integrations of these materials are also given. Such metal nanostructure-based transparent electrodes are particularly attractive for solar cell applications.

Reducing our dependence on fossil fuels increases the demand for energy storage. Lithium-ion batteries have transformed portable electronics and will continue to be important but cannot deliver the step change in energy density required in the longer term in markets such as electric vehicles and the storage of electricity from renewables. There are a few alternatives. Here we describe two: Li-air and Li-sulfur batteries. We compare the energy densities of Li-ion, Li-air, and Li-S and discuss their differences and the challenges facing Li-air and Li-S, many of which are materials related.

Hydrogen generation using solar energy will require the development of efficient electrocatalysts for proton reduction. This article discusses the important role that proton movement plays in hydrogenase enzymes and potential devices for solar generation. Studies of hydrogenase enzymes provide many important design principles for the development of simpler molecular catalysts. These principles are illustrated with examples from the literature and from the authors’ laboratories. In particular, pendant bases incorporated in the second coordination sphere of catalytic molecules play a number of important roles that are crucial to efficient catalysis. These roles include acting as relays to move protons between the metal center and solution, promoting intra- and intermolecular proton transfer reactions, coupling proton and electron transfer reactions, assisting heterolytic cleavage of hydrogen, and stabilizing critical reaction intermediates. The importance of controlling proton movement on the molecular scale underscores the importance of a similar degree of control in devices designed for the solar production of hydrogen or any fuel generation process involving multiple electrons and protons.

Atomic layer deposition (ALD) not only presents a direct way to prepare nanomaterials when combined with templates, but also allows surface engineering to fine-tune the properties of the material. Here, we review recent progress in the field of nanostructured materials and devices that have been fabricated by ALD. Various materials, including semiconducting, magnetic, noble metallic, and insulating materials, can be used to form three-dimensional (3D), complex nanostructures with controlled composition and physical properties. We begin this review with ALD nanomaterials that can be prepared from porous templates with a 2D pore arrangement, such as anodic aluminum oxide, and advance toward opal structures with a 3D pore arrangement. We also discuss surface engineering by ALD on existing nanowires/nanotubes, devices, and chemical patterns that has the potential for application in high-performance transistors, sensors, and green energy conversion. Finally, we provide perspectives for future device applications that could arise from ALD nanomaterials.

Educational outreach efforts for K–12 students, ages 5–18, are becoming increasingly visible, active, and pervasive in the materials science community as a result of funding agency requirements in the United States and gradual institutional attitudinal shifts toward placing a higher emphasis on engaging non-technical audiences. Many scientists recognize it as both an obligation and a pleasure to share their research with young audiences. However, in addition to enthusiasm and funding agency mandates, equally essential to successful educational outreach projects are effective, engaging educational materials and programs. Hands-on demonstrations, classroom lesson plans, summer research internships, and education-oriented laboratory experiments are just a few examples of the wide variety of possibilities from which materials scientist educators can currently choose. This article addresses the process of developing educational outreach activities and programs, including setting goals, establishing partnerships, and planning for and implementing outreach activities for students. Examples from the materials science outreach community are integrated to illustrate implementations of these ideas and to offer ideas for collaborations and future projects.